1. Field of the Invention
The present invention relates to a radial-type ceramic turbine rotor and a method for producing the same.
2. Description of the Prior Art
Silicon ceramics, such as silicon nitride, silicon carbide, sialon and the like, are more stable than metal at high temperatures, and have high resistance against oxidation, corrosion and creep deformation. Therefore, there has been investigation into the utilization of silicon ceramics in engine parts. Particularly, a radial-type turbine rotor consisting of a ceramic material is lighter in weight than a metal rotor, can operate at a temperature higher than a metal rotor, and has better heat efficiency than a metal rotor. Therefore, radial-type ceramic turbine rotors have recently become attractive as a turbo-charger rotor for automobiles, gas-turbine rotors and the like.
There has hitherto been known a radial-type ceramic turbine rotor disclosed in Japanese Patent Laid-open Specification No. 88,201/82, which corresponds to U.S. Pat. No. 4,544,327. This turbine rotor has been produced by a method, wherein a blade member 1 having a complicated three-dimensional shape is formed from ceramics, for example, by an injection molding; a shaft 2 is produced by means of a rubber press from a green body of the shaft, which has been obtained from ceramics, for example, by means of a metal mold press; and the resulting blade member 1 and shaft 2 are conically fitted and bonded to each other, and the bonded article is fired to form a monolithic ceramic turbine rotor as illustrated in FIG. 2. However, the ceramic turbine rotor produced by the method disclosed in this prior art has drawbacks that (1) cracks are likely to form during the dewaxing step in the large thickness portion of a shaped article for blade member produced by the injection molding; (2) it is necessary to match exactly the shape of the blade member with that of the shaft at their portion, and when their shapes are not matched with each other, gaps and other bondings defects occur in the bonding interface, and moreover the thickness of the paste applied to the bonding interface is apt to be ununiform, resulting in a decrease of the bonding strength; and (3) it is difficult to determine the center hole of a fired rotor during precision machining thereof, and the fired rotor is poor in workability, and the like.